Catheter with atraumatic tip

ABSTRACT

A medical device is provided comprising a shaft comprising a first segment and a second segment. The first segment is configured to buckle upon application of a first critical force. The second segment includes an outer surface and an inner surface and is configured to buckle upon application of a second critical force. The second critical force is lower than the first critical force. The medical device further comprises a coil disposed radially inwardly of the inner surface of the second segment.

BACKGROUND OF THE INVENTION

a. Field of the Invention

The instant disclosure relates generally to medical devices. Inparticular, the instant disclosure relates to elongate medical devicesconfigured to buckle upon application of a critical force.

b. Background Art

Electrophysiology catheters are used in a variety of diagnostic,therapeutic, and/or mapping and ablative procedures to diagnose and/orcorrect conditions such as atrial arrhythmias, including for example,ectopic atrial tachycardia, atrial fibrillation, and atrial flutter.Arrhythmias can create a variety of conditions including irregular heartrates, loss of synchronous atrioventricular contractions and stasis ofblood flow in a chamber of a heart which can lead to a variety ofsymptomatic and asymptomatic ailments and even death.

Typically, a catheter is deployed and manipulated through a patient'svasculature to the intended site, for example, a site within a patient'sheart or a chamber or vein thereof. The catheter carries one or moreelectrodes that can be used for cardiac mapping or diagnosis, ablationand/or other therapy delivery modes, or both, for example. Once at theintended site, treatment can include, for example, radio frequency (RF)ablation, cryoablation, laser ablation, chemical ablation,high-intensity focused ultrasound-based ablation, microwave ablation,and/or other ablation treatments. The catheter imparts ablative energyto cardiac tissue to create one or more lesions in the cardiac tissueand oftentimes a contiguous or linear and transmural lesion. This lesiondisrupts undesirable cardiac activation pathways and thereby limits,corrals, or prevents errant conduction signals that can form the basisfor arrhythmias. According to at least one medical study (See, e.g.,Ikeda et al., Radiofrequency Ablation Catheter with Contact Force SensorPredicts Lesion Size and Incidence of Steam Pop in the Beating CanineHeart, Conference Proceedings of the Hearth Rhythm Society, May 2008 andThiagalingam et al., Importance of Catheter Contact Force DuringIrrigated Radiofrequency Ablation: Evaluation in a Porcine Ex Vivo ModelUsing a Force-Sensing Catheter, Journal of CardiovascularElectrophysiology, February 2010), the therapeutic force required tocreate a transmural lesion can be about 20 to about 50 grams-force.

To position a catheter within the body at a desired site, some type ofnavigation must be used, such as using mechanical steering featuresincorporated into the catheter (or an introducer sheath). In someexamples, medical personnel may manually manipulate and/or operate thecatheter using the mechanical steering features, and in other examples arobotic system may be used to manipulate and/or operate the catheter.Recent advances in the robotic control of catheters and the like allowadvancement, retraction, and various deflections and/or steering to becontrolled robotically.

In order to facilitate the advancement of catheters through a patient'svasculature, the simultaneous application of torque at the proximal endof the catheter and the ability to selectively deflect the distal tip ofthe catheter in a desired direction can permit medical personnel (eitherthrough manual operation or through robotic control) to adjust thedirection of advancement of the distal end of the catheter and toposition the distal portion of the catheter during anelectrophysiological procedure. The proximal end of the catheter can bemanipulated to guide the catheter through a patient's vasculature. Thedistal tip can be deflected by a pull wire attached at the distal end ofthe catheter that extends to a control handle or robotic system thatcontrols the application of tension on the pull wire.

In catheter designs, it can be important to have sufficient flexibilityin the catheter shaft to allow the catheter to follow the inherentcurvature of the vasculature or endocardium without puncturing vasculartissue and/or cardiac tissue. The perforation of vascular tissue and/orcardiac tissue during cardiac mapping can be a problem in the practiceof cardiac electrophysiology. A perforation in the cardiac tissue canresult in pericardial effusion or the abnormal accumulation of fluid inthe pericardial space and possible cardiac tamponade, which can be lifethreatening to the patient. The myocardium of the left atrium of theheart is particularly thin and is susceptible to perforation. Accordingto at least one medical study (See, e.g., Shah et al., Catheter TipForce Required to Mechanically Perforate the Cardiac Free Wall,Conference Proceedings of the Hearth Rhythm Society, May 2008),perforation of cardiac tissue can begin to occur with about 100grams-force. However, other medical studies indicate that perforation ofcardiac tissue may begin to occur with even less than about 100grams-force.

Current catheter designs have concentrated on the use of force orcontact sensing to carefully monitor and thereby limit the amount offorce delivered during ablation in order to create safe and efficaciouslesions. However, such force or contact sensing designs may notconsistently provide completely accurate force measurements and canpotentially register false positive detections of excessive force andfalse negatives in which excessive force is not preemptively avoided.Moreover, force or contact sensing systems may report a high forcedetection too late to prevent perforation. When a high force isgenerated, even if this force is reported instantaneously by the forceor contact sensing systems, the damage may have been caused immediatelygiving the operator no opportunity to reduce the force.

There is therefore a need to minimize and/or eliminate one or more ofthe problems as set forth above. A preferable solution would be to avoidthe problem of high catheter force altogether.

BRIEF SUMMARY OF THE INVENTION

It is desirable to design a catheter having a mechanical solution forlowering the risk or reducing the likelihood of the catheter fromperforating cardiac tissue, rather than being solely dependent on forceor contact sensing to identify when a threshold amount of force is beingapplied to the catheter that is likely to result in perforation ofcardiac tissue. In particular, it would be desirable to design acatheter having at least a portion thereof with a relatively low maximumor critical force that causes buckling. It would be desirable for atleast a portion of the catheter to be configured to transmit sufficienttherapeutic force to create a transmural lesion, while still beingconfigured to buckle upon application of a force that would besufficient to perforate cardiac tissue or upon application of a forcelower than that which would be sufficient to perforate cardiac tissue.Accordingly, it would be desirable for the maximum or critical forcethat causes buckling of the catheter to be between the maximum amount offorce required to create a transmural lesion (e.g., about 50 grams-forceaccording to some medical studies, although other amounts may bepossible) and the minimum amount of force that can cause perforation ofthe cardiac wall (e.g., about 100 grams-force according to some medicalstudies or even about 50 grams-force according to other medicalstudies). For example and without limitation, it would be desirable forat least a portion of the catheter to be configured to buckle uponapplication of a maximum or critical force that is about 50 grams-forceto about 100 grams-force. A catheter configured to buckle under amaximum or critical force that causes buckling between about 50grams-force to about 100 grams-force can develop enough force to createa transmural lesion without buckling, but can predictably buckle priorto developing enough force to perforate cardiac tissue. Although a rangefor the maximum or critical force that causes buckling of a catheter inaccordance with an exemplary embodiment of the disclosure is disclosedas being between about 50 grams-force to about 100 grams-force, therange for the maximum or critical force that causes buckling may belower or higher in accordance with other embodiments of the disclosure.For example and without limitation, the range for the maximum orcritical force that causes buckling of a catheter in accordance withother exemplary embodiments of the disclosure can be about 50 to about60 grams-force in some embodiments. For example and without limitation,the range for the maximum or critical force that causes buckling of acatheter in accordance with other exemplary embodiments of thedisclosure can be about 20 grams-force to about 50 grams-force in someembodiments. For example and without limitation, the maximum or criticalforce that causes buckling of a catheter in accordance with otherexemplary embodiments of the disclosure can be about 40 grams-force insome embodiments.

A medical device is provided comprising a shaft comprising a firstsegment and a second segment. The first segment can have an outersurface and an inner surface. The first segment can be configured tobuckle upon application of a first critical force thereto. The secondsegment can include an outer surface and an inner surface. The secondsegment is configured to buckle upon application of a second criticalforce thereto, wherein the second critical force is lower than the firstcritical force. For example and without limitation, the second criticalforce is in the range of about 40 grams-force to about 100 grams-force.The second segment can be configured to transmit force in the range ofat least about 20 grams-force to about 50 grams-force to tissuecontacting the second segment. For example and without limitation thesecond segment comprises polyether block amides. For example and withoutlimitation, the second segment has a hardness between about 25 and about35 on a Shore D scale. Although a first and second segment are mentionedin detail, the medical device can include additional segments inaccordance with various embodiments of the disclosure. For example andwithout limitation, the medical device can include a third segmentconfigured to buckle upon application of a third critical force thereto.The third critical force can be different than both the first criticalforce and the second critical force. The third segment can also includean outer surface and an inner surface.

In accordance with some embodiments of the disclosure, the secondsegment has a distal end formed in the shape of a pigtail. In accordancewith other embodiments of the disclosure, the second segment has atleast one electrode disposed on the second segment. For example andwithout limitation, the a first electrode can be disposed on the distalend of the second segment. Additional electrodes may be disposed on thesecond segment proximally of the first electrode. In an embodiment ofthe disclosure, the second segment may include about four electrodes.

The medical device further comprises a coil disposed radially inwardlyof the inner surface of the second segment. The coil can be separatefrom the first segment and from the second segment in accordance withsome embodiments of the disclosure. The coil can be configured toprevent collapsing of an irrigation lumen within the coil. The coil canalso be configured to maintain the amount of force transmitted by thesecond segment to tissue contacting the second segment even after anapplication of the second critical force to the second segment. The coilcan have a proximal end and a distal end. In some embodiments of thedisclosure, spacing between adjacent turns of the coil is greater at thedistal end of the coil than the proximal end of the coil. In someembodiments of the disclosure, a first diameter of the coil at theproximal end is greater than a second diameter of the coil at the distalend. In some embodiments of the disclosure, at least a portion of theproximal end of the coil is welded to the second segment and at least aportion of the distal end of the coil is welded to the second segment.

In some embodiments of the disclosure, the second segment of the medicaldevice may further comprise a curve at a select location along a lengthof the medical device. For example and without limitation, the curve canbe in the range of about 5 degrees to about 25 degrees in someembodiments of the disclosure. For example and without limitation, thecurve can be defined by the angle between a first portion of the medicaldevice on a first side of the curve and a second portion of the medicaldevice on a second opposing side of the curve. In some embodiments ofthe disclosure, the medical device can further comprise a fluid lumendisposed radially inwardly of the coil. In some embodiments of thedisclosure, the medical device can further comprise a force/contactsensor configured to detect an amount of force provided by the medicaldevice. In some embodiments of the disclosure, the second segment cancomprise a first critical section on which a first plurality ofelectrodes are disposed and a second critical section on which a secondplurality of electrodes are disposed. The medical device can furthercomprise a sensor configured to generate a signal indicative of a bendangle between the first critical section and the second critical sectionof the second segment.

A medical device is provided comprising a shaft comprising a firstsegment and a second segment. The first segment is configured to buckleupon application of a first critical force thereto. The second segmentis configured to buckle upon application of a second critical forcethereto. The second critical force is lower than the first criticalforce and is in the range of about 40 grams-force to about 100grams-force. The medical device can further comprise at least oneelectrode disposed on at least one of the first and second segments ofthe shaft. The medical device can further comprise a coil disposedradially inwardly of an inner surface of the second segment, wherein thecoil is separate from both the first segment and the second segment, andwherein the second segment is configured to transmit force in the rangeof at least about 20 grams-force to about 50 grams-force to tissuecontacting the second segment after application of the second criticalforce to the second segment. The medical device can further comprise afluid lumen disposed radially inwardly of the coil.

A medical device is provided comprising a shaft comprising a firstsegment and a second segment. The first segment is configured to buckleupon application of a first critical force thereto. The second segmentis configured to buckle upon application of a second critical forcethereto. The second critical force is lower than the first criticalforce. The medical device can further comprise a means for maintainingthe amount of force transmitted by the second segment to tissuecontacting the second segment after an application of the secondcritical force to the second segment. The medical device can furthercomprise a means for preferentially buckling the second segment in aselect manner, such as a deflection preference element comprising acurve at a select location along the length of the medical device.

The foregoing and other aspects, features, details, utilities, andadvantages of the present disclosure will be apparent from reading thefollowing description and claims, and from reviewing the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a medical device in accordance with afirst embodiment of the disclosure.

FIG. 2 is a cross-sectional view of the medical device of FIG. 1.

FIG. 3 is a cross-sectional view of a medical device in accordance witha second embodiment of the disclosure.

FIG. 4 is a partially transparent perspective view of a distal segmentof a medical device according to various embodiments of the disclosure.

FIG. 5 is a schematic view of a medical device in accordance with athird embodiment of the disclosure.

FIG. 6 is an isometric diagrammatic view of an electrode of the medicaldevice of FIG. 1 illustrating an exemplary force/contact sensor assemblyin accordance with a fourth embodiment of the disclosure.

FIG. 7 is a schematic view of a medical device in accordance with afifth embodiment of the disclosure.

FIG. 8 is an exemplary graph showing force as a function of the forwarddisplacement of the medical device of FIG. 1.

DETAILED DESCRIPTION OF THE DISCLOSURE

Various embodiments are described herein to various apparatuses,systems, and/or methods. Numerous specific details are set forth toprovide a thorough understanding of the overall structure, function,manufacture, and use of the embodiments as described in thespecification and illustrated in the accompanying drawings. It will beunderstood by those skilled in the art, however, that the embodimentsmay be practiced without such specific details. In other instances,well-known operations, components, and elements have not been describedin detail so as not to obscure the embodiments described in thespecification. Those of ordinary skill in the art will understand thatthe embodiments described and illustrated herein are non-limitingexamples, and thus it can be appreciated that the specific structuraland functional details disclosed herein may be representative and do notnecessarily limit the scope of the embodiments, the scope of which isdefined solely by the appended claims.

Reference throughout the specification to “various embodiments,” “someembodiments,” “one embodiment,” or “an embodiment”, or the like, meansthat a particular feature, structure, or characteristic described inconnection with the embodiment is included in at least one embodiment.Thus, appearances of the phrases “in various embodiments,” “in someembodiments,” “in one embodiment,” or “in an embodiment”, or the like,in places throughout the specification are not necessarily all referringto the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments. Thus, the particular features, structures, orcharacteristics illustrated or described in connection with oneembodiment may be combined, in whole or in part, with the featuresstructures, or characteristics of one or more other embodiments withoutlimitation given that such combination is not illogical ornon-functional.

It will be appreciated that the terms “proximal” and “distal” may beused throughout the specification with reference to a clinicianmanipulating one end of an instrument used to treat a patient. The term“proximal” refers to the portion of the instrument closest to theclinician and the term “distal” refers to the portion located furthestfrom the clinician. It will be further appreciated that for concisenessand clarity, spatial terms such as “vertical,” “horizontal,” “up,” and“down” may be used herein with respect to the illustrated embodiments.However, surgical instruments may be used in many orientations andpositions, and these terms are not intended to be limiting and absolute.

The instant disclosure generally relates to irrigated ablation electrodeassemblies. For purposes of this description, similar aspects among thevarious embodiments described herein will be referred to by similarreference numbers. As will be appreciated, however, the structure of thevarious aspects can be different among the various embodiments.

Referring now to FIG. 1, a schematic view of a medical device 10 inaccordance with an embodiment of the disclosure is illustrated withdifferences in cross-hatching showing potential differences in materialsand/or structure. The medical device 10 may be a catheter comprising anelongated shaft 12 having a first segment 14 and a second segment 16.Although a medical device 10 comprising two segments 14, 16 arementioned in detail, additional segments can be utilized in connectionwith medical device 10 in accordance with various other embodiments ofthe invention. Also, although the embodiment shown in FIG. 1 depictsmedical device 10 as a catheter, it can be appreciated that the medicaldevice 10 can comprise any medical device designed to pass through anopening or body lumen. For example and without limitation, the medicaldevice 10 can comprise catheters (e.g., therapeutic, diagnostic, and/orguide catheters), sheaths, introducers (e.g., steerable and/or precurvedintroducers), epicardial devices, endoscopic devices, laproscopicdevices, as well as any other medical devices. While the devices and/ormethods described herein may be especially useful in connection withrobotically controlled systems, such devices and/or methods can also beincorporated in connection with manually manipulated medical devices inorder to provide an added level of safety for the physician and patient,for example.

The length of medical device 10, shaft 12, first segment 14, and/orsecond segment 16 or portions thereof are typically dictated by thelength and flexibility characteristics desired in the final medicaldevice 10. The cross-sectional shape of medical device 10, shaft 12,first segment 14, and/or second segment 16 or portions thereof aretypically dictated by the desired characteristics (e.g., flexibility,torque transmission characteristics, etc.) in the final medical device10 and can vary in accordance with various embodiments of thedisclosure. For example, they can have a substantially roundcross-sectional shape in some embodiments. However, othercross-sectional shapes or combinations of shapes can be utilized inaccordance with other embodiments of the disclosure. For example, thecross-sectional shapes can be oval, rectangular, square, polygonal, orany other suitable shape, or combinations thereof. The diameter ofmedical device 10, shaft 12, first segment 14, and/or second segment 16or portions thereof are also typically dictated by the desiredcharacteristics (e.g., flexibility, torque transmission characteristics,etc.) in the final medical device 10 and can vary in accordance withvarious embodiments of the disclosure. For example, they can have asubstantially constant diameter in some embodiments or can have avariable diameter in other embodiments (e.g., linear tapered regions,curvilinear tapered regions, step-wise tapered regions, etc.). Forexample and without limitation, the medical device 10 can comprise anintracardiac catheters having a diameter of about 8 French or less.

In accordance with an embodiment of the disclosure, the first segment 14can be a proximal segment of the shaft 12, and the second segment 16 canbe a distal segment of the shaft 12. Although this particularconfiguration is mentioned in detail, in accordance with otherembodiments of the disclosure, the first segment 14 can be a distalsegment of the shaft 12, and the second segment 16 can be a proximalsegment of the shaft 12.

Referring now to FIG. 2, the first segment 14 includes an outer surface18 and an inner surface 20. The first segment 14 can comprise a polymerin accordance with an embodiment of the disclosure. The polymer cancomprise, for example and without limitation, polyether block amidessuch as those sold under the trademark PEBAX® and generally availablefrom Arkema France. Although polyether block amides are mentioned indetail, the polymer can comprise any number of other polymers such aspolytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP),polyurethane, polypropylene (PP), polyvinylchloride (PVC),polyether-ester (for example a polyether-ester elastomer such asARNITEL® available from DSM Engineering Plastics), polyester (forexample a polyester elastomer such as HYTREL® available from DuPont),polyamide (for example, DURETHAN® available from Bayer or CRISTAMID®available from Elf Atochem), elastomeric polyamides, blockpolyamide/ethers, silicones, polyethylene, Marlex high-densitypolyethylene, linear low density polyethylene (for example REXELL®),polyetheretherketone (PEEK), polyimide (PI), polyetherimide (PEI), othersuitable materials, or mixtures, combinations, or copolymers thereof. Insome embodiments the first segment 14 can include a liquid crystalpolymer (LCP) blended with other polymers to enhance torqueability.Although polymers are mentioned in detail, the first segment 14 cancomprise any other number of materials in other embodiments. For exampleand without limitation, the first segment 14 can comprise metals, metalalloys, polymers, or combinations or mixtures thereof. Some examples ofsuitable metals and metal alloys include stainless steel, such as 304vstainless steel; nickel-titanium alloy, such as “Nitinol,”nickel-chromium alloy, nickel-chromium-iron 65 alloy, cobalt alloy, orthe like; or other suitable material. The entire first segment 14 can bemade of the same material, or the composition of the first segment 14can vary along a length of the first segment 14. At least a portion ofthe material comprising the first segment 14 can be contoured (e.g.,laser cut) to provide unique shapes that can have rotational rigidity,but have low column strength or other desirable characteristics inaccordance with some embodiments of the disclosure. For example andwithout limitation, at least a portion of the material comprising thefirst segment 14 can comprise a helically shaped body having alternatelyspaced projections extending away from the helically shaped body inopposite directions from one another along the length of the helix. Forexample, a first set of projections can extend distally, and a secondset of projections can extend proximally, with the first set ofprojections offset from and positioned between the second set ofprojections. Recesses extending between projections can be inverselyshaped with respect to an outer contour of the projections. Theprojections and recesses can be trapezoidal in shape in accordance withsome embodiments of the disclosure, but other shapes for the projectionsand recesses could be used in alternative embodiments. The projectionsmay extend into recesses from an adjacent section of the helical body toform an interlocking arrangement.

In general, the first segment 14 can comprise materials chosen to ensurethat the first segment 14 is relatively stiff for pushability andtorqueability. For example and without limitation, the first segment 14can have a hardness between about 60 and about 90 on a Shore D scale.For example and without limitation, the first segment 14 can have aShore D durometer of about 75. Although these particular amounts aredisclosed for the hardness of the first segment 14, the hardness of thefirst segment 14 can be greater or less in accordance with variousembodiments of the disclosure. The entire first segment 14 can have thesame Shore D durometer in an embodiment of the disclosure, or thehardness of the first segment 14 can vary along the length of the firstsegment 14 in accordance with other embodiments of the disclosure. Thefirst segment 14 has a first critical force sufficient to cause bucklingof the first segment 14. For example and without limitation, the firstcritical force sufficient to cause buckling of the first segment 14 canbe greater than 100 grams-force. In particular, the first critical forcesufficient to cause buckling of the first segment 14 can be betweenabout 200 grams-force and about 660 grams-force. Although theseparticular amounts are disclosed for the first critical force, the firstcritical force of the first segment 14 can be greater or less inaccordance with various embodiments of the disclosure. The entire firstsegment 14 can be configured to have the same first critical force, orthe first critical force of the first segment 14 can vary along thelength of the first segment 14. The first critical force can befine-tuned to any desired range by altering the durometer of thematerials used for the first segment 14 and/or modifying theconfiguration of the first segment 14 through the use of laser-cutting,for example.

Now referring to FIGS. 1-2, the second segment 16 includes an outersurface 22 and an inner surface 24. The second segment 16 furtherincludes a distal end 26 and a proximal end 28. The second segment 16can comprise a polymer in accordance with an embodiment of thedisclosure. The polymer can comprise, for example and withoutlimitation, polyether block amides such as those sold under thetrademark PEBAX® and generally available from Arkema France. Althoughpolyether block amides are mentioned in detail, the polymer can compriseany number of other polymers such as PTFE, FEP, polyurethane, PP, PVC,polyether-ester (for example a polyether-ester elastomer such asARNITEL® available from DSM Engineering Plastics), polyester (forexample a polyester elastomer such as HYTREL® available from DuPont),polyamide (for example, DURETHAN® available from Bayer or CRISTAMID®available from Elf Atochem), elastomeric polyamides, blockpolyamide/ethers, silicones, polyethylene, Marlex high-densitypolyethylene, linear low density polyethylene (for example REXELL®),PEEK, PI, PEI, other suitable materials, or mixtures, combinations, orcopolymers thereof. In some embodiments the second segment 16 caninclude an LCP blended with other polymers to enhance torqueability.Although polymers are mentioned in detail, the second segment 16 cancomprise any other number of materials in other embodiments. For exampleand without limitation, the second segment 16 can comprise metals, metalalloys, polymers, or combinations or mixtures thereof. Some examples ofsuitable metals and metal alloys include stainless steel, such as 304vstainless steel; nickel-titanium alloy, such as “Nitinol,”nickel-chromium alloy, nickel-chromium-iron 65 alloy, cobalt alloy, orthe like; or other suitable material. The entire second segment 16 canbe made of the same material, or the composition of the second segment16 can vary along a length of the second segment 16. At least a portionof the material comprising the second segment 16 can be contoured (e.g.,laser cut) to provide unique shapes that can have rotational rigidity,but have low column strength or other desirable characteristics inaccordance with some embodiments of the disclosure. For example andwithout limitation, at least a portion of the material comprising thesecond segment 16 can comprise a helically shaped body havingalternately spaced projections extending away from the helically shapedbody in opposite directions from one another along the length of thehelix. For example, a first set of projections can extend distally, anda second set of projections can extend proximally, with the first set ofprojections offset from and positioned between the second set ofprojections. Recesses extending between projections can be inverselyshaped with respect to an outer contour of the projections. Theprojections and recesses can be trapezoidal in shape in accordance withsome embodiments of the disclosure, but other shapes for the projectionsand recesses could be used in alternative embodiments. The projectionsmay extend into recesses from an adjacent section of the helical body toform an interlocking arrangement.

The second segment 16 generally provides the medical device 10 with aregion having decreased column strength or increased flexibility ascompared to the first segment 14. For example and without limitation,the second segment 16 can have a hardness between about 25 and about 35on a Shore D scale. In a preferred embodiment, the second segment 16 canhave a Shore D durometer of about 25. Although these particular amountsare disclosed for the hardness of the second segment 16, the hardness ofthe second segment 16 can be greater or less in accordance with variousembodiments of the disclosure. The entire second segment 16 can have thesame Shore D durometer in some embodiments of the disclosure, or thehardness of the second segment 16 can vary along the length of thesecond segment 16 in other embodiments of the disclosure. Because of itsdecreased Shore D durometer hardness, the second segment 16 is moreflexible than first segment 14. This feature allows medical device 10 tobuckle at second segment 16.

The second segment 16 may be configured so that it can buckle uponapplication of a second critical force to the second segment 16. Thesecond critical force can be applied to the second segment 16 of themedical device 10 at any approach angle of the medical device 10. Forexample and without limitation, the application of the second criticalforce at a glancing angle can have a component of force along the axisof the medical device 10 and a component of force tangent to thedirection of the second segment 16 of the medical device 10.Mechanically, it is the tangential component of the force that causesthe buckling of the second segment 16. For another example and withoutlimitation, the application of the second critical force on the axis ofthe medical device 10 (e.g., straight on) can have at least a momentarytangential force that can cause the cascade of failure (e.g., buckling)to occur. Buckling is generally understood to be a change in shape ofthe medical device 10 or any other type of altering of position or ofconfiguration of medical device 10 that results in at least some lateraldisplacement of at least a portion of second segment 16. Althoughlateral deflection is mentioned in detail, other forms of buckling caninclude spiraling, looping, or helical buckling. Buckling of the secondsegment 16 can divert force away from or prevent force from beingdirectly or indirectly transmitted from second segment 16 to cardiactissue. Diverting or preventing the transmission of force to cardiactissue can result in a reduced or nominal amount of displacement of thecardiac tissue. As force is applied to the first segment 14 of themedical device 10 in the distal direction, the medical device 10advances distally. When additional distal force is diverted from thecardiac tissue by the buckling of second segment 16, the second segment16 acts to limit the amount of force that can be transmitted from thefirst segment 14 to the cardiac tissue, thereby helping to avoidundesirable perforation of the cardiac tissue. Buckling of the secondsegment 16 can also increase the surface area of the medical device 10in contact with the tissue, thereby distributing the applied force overa greater area and reducing pressure, which provides an additionalsafety factor. Buckling of the second segment 16 can also increasecontact area during ablation, which can create large lesions. Inaddition, the second segment 16 can be configured to absorb any energycaused by the medical device 10 making contact with tissue under cardiacmotion which might otherwise cause the medical device 10 to lose contactwith the tissue, thereby allowing the medical device 10 to be kept incontact with the tissue even under cardiac motion and providing auniform force. Accordingly, the second segment 16 can prevent themedical device 10 from breaking contact during ablation/mapping forbetter lesions and recordation of cardiac signals.

As noted above, the second segment 16 may be configured so that it canbuckle upon application of a second critical force to the second segment16. The second critical force of the second segment 16 is lower than thefirst critical force of the first segment 14. The second critical forcethat causes buckling of the second segment 16 of the medical device 10is configured to be between the amount of force required to create atransmural lesion (i.e., about 20 to about 50 grams-force according tosome medical studies, but can be more or less) and the minimum amount offorce that can cause perforation of cardiac tissue (i.e., about 100grams-force according to some medical studies and even about 50grams-force according to other medical studies). For example and withoutlimitation, the second critical force sufficient to cause buckling ofthe second segment 16 of the medical device 10 can be in the range ofabout 40 grams-force to about 100 grams-force. Although these particularamounts are disclosed for the second critical force, the second criticalforce of the second segment 16 can be greater or less in accordance withvarious embodiments of the disclosure. For example and withoutlimitation, the second critical force sufficient to cause buckling ofthe second segment 16 of the medical device 10 can be in the range ofabout 50 grams-force to about 60 grams-force in accordance with someembodiments of the disclosure. For example and without limitation, thesecond critical force sufficient to cause buckling of the second segment16 of the medical device 10 can be in the range of about 20 grams-forceto about 50 grams-force in accordance with some embodiments of thedisclosure. For example and without limitation, the second criticalforce sufficient to cause buckling of the second segment 16 of themedical device 10 can be about 40 grams-force. The second segment 16 canbe configured to develop and transmit sufficient force to targetedcardiac tissue to create a transmural lesion in cardiac tissue withoutbuckling, but would be configured to predictably buckle prior todeveloping and transmitting force sufficient to perforate cardiactissue. In this way, the second segment 16 can be engineered to buckleat a predetermined second critical force and/or be tuned to buckle at aspecific force. For example, it can be desirable to manufacture orconfigure the second segment 16 so that it will buckle before thepushing forces become high enough that second segment 16 could displaceand perforate, for example, a blood vessel or other cardiac tissue. Theentire second segment 16 can be configured to have the same secondcritical force, or the second critical force of the second segment 16can vary along the length of the second segment 16. The second criticalforce can be fine-tuned to any desired range by altering the durometerof the materials used for the second segment 16 and/or modifying theconfiguration of the second segment 16 through the use of laser-cutting,for example. Although the medical device 10 is described and generallyillustrated as including one second segment 16, the medical device 10can include any number of segments, zones, and/or locations having acritical force sufficient to cause buckling of the segment, zone, and/orlocation that is lower than the first critical force of the firstsegment 14. In this way, the medical device 10 can have one or more suchsegments, zones, and/or locations configured for buckling. For exampleand without limitation, as generally illustrated in FIG. 7, a medicaldevice 10′ can comprise a third segment 15. The third segment 15 canalso include an inner surface and an outer surface. The third segment 15can be configured to buckle upon application of a third critical force.The third critical force can be different than the first critical forcein accordance with some embodiments of the disclosure. The thirdcritical force can be different than the second critical force inaccordance with some embodiments of the disclosure. FIG. 8 is anexemplary graph showing force as a function of the forward displacementof the medical device 10, 10′ after the medical device comes intocontact with tissue. For example and without limitation, FIG. 8generally illustrates a rise in force that asymptotically approaches thesecond critical force or buckling force.

Still referring to FIGS. 1-2, the medical device 10 can comprise one ormore electrodes disposed on the second segment 16. Although one or moreelectrodes being disposed on the second segment 16 is mentioned indetail, one or more electrodes can be disposed on the first segment 14in accordance with some embodiments of the disclosure. A first electrode30 can be disposed on the distal end 26 of the second segment 16 inaccordance with an embodiment of the disclosure. The first electrode 30can comprise an ablation electrode disposed at the extreme distal end 26of the second segment 16 and can be referred to as a tip electrode. Adistal end of the first electrode 30 can be partially spherical orgenerally hemispherical in shape in accordance with an embodiment of thedisclosure. Electrode 30 can comprise an electrically conductivematerial that can be generally resistant to corrosion and isbiocompatible. For example and without limitation, electrode 30 can beconstructed from platinum. However, other conductive materials, such asgold, stainless steel, or others known in the art can be similarly used.The first electrode 30 can include a corresponding conductor.

In accordance with some embodiments of the disclosure, the distal end 26of the second segment 16 can comprise a tip element as described andillustrated in at least FIG. 9 of U.S. Patent Application PublicationNo. 2010/0174177 entitled “Magnetically Guided Catheter,” the entiredisclosure of which is incorporated herein. In such an embodiment of thedisclosure, the tip element can comprise a helically shaped body havingalternately spaced projections extending away from the helically shapedbody in opposite directions from one another along the length of thehelix. For example, a first set of projections can extend distally, anda second set of projections can extend proximally, with the first set ofprojections offset from and positioned between the second set ofprojections. Recesses extending between projections can be inverselyshaped with respect to an outer contour of the projections. Theprojections and recesses can be trapezoidal in shape in accordance withsome embodiments of the disclosure, but other shapes for the projectionsand recesses could be used in alternative embodiments. The projectionsmay extend into recesses from an adjacent section of the helical body toform an interlocking arrangement.

At least a second electrode 32 can be disposed on the second segment 16of the medical device 10 in accordance with an embodiment of thedisclosure. The second electrode 32 can be disposed proximally of thefirst electrode 30. A plurality of electrodes (e.g., second electrode32, third electrode 34, and fourth electrode 36) can be disposed on thesecond segment 16 of the medical device 10 in accordance with anembodiment of the disclosure. The plurality of electrodes 32, 34, 36 canbe disposed along a longitudinal axis A of the medical device 10. Secondelectrode 32 can be disposed proximally of the first electrode 30, thirdelectrode 34 can be disposed proximally of the second electrode 32, andfourth electrode 34 can be disposed proximally of the third electrode34. Each of the plurality of electrodes 32, 34, 36 can comprise anelectrically conductive material that can be generally resistant tocorrosion and is biocompatible. For example and without limitation, eachelectrode 32, 34, 36 can be constructed from platinum. However, otherconductive materials, such as stainless steel or others known in the artcan be similarly used. Each of the plurality of electrodes 32, 34, 36can comprise a ring electrode as generally known in the art inaccordance with some embodiments of the disclosure. Each of theplurality of electrodes 32, 34, 36 can include a corresponding wireextending toward a proximal end of the medical device 10 for connectionto an energy generator in accordance with some embodiments of thedisclosure.

Each of electrodes 32, 34, 36 can comprise a positioning electrode used,for example, with a visualization, navigation, and mapping system andcan be configured to provide a signal indicative of a position and/ororientation of at least a portion of the medical device 10. Thevisualization, navigation, and/or mapping system with which theelectrodes 32, 34, 36 can be used can comprise an electric field-basedsystem, or sometimes referred to as an impedance-based system, such as,for example, that having the name ENSITE NAVX™ (aka ENSITE™ ‘Classic’ aswell as newer versions of the ENSITE™ system, denoted as ENSITEVELOCITY™) and available from St. Jude Medical, Inc. and as generallyshown with reference to U.S. Pat. No. 7,263,397 entitled “Method andApparatus for Catheter Navigation and Location and Mapping in theHeart,” the entire disclosure of which is incorporated herein byreference. In accordance with an electric field-based system, theelectrodes 32, 34, 36 can be configured to be responsive to an electricfield transmitted within the body of the patient. The electrodes 332,34, 36 can be used to sense an impedance at a particular location andtransmit a representative signal to an external computer or processor.In other exemplary embodiments, however, the visualization, navigation,and/or mapping system can comprise other types of systems, such as, forexample and without limitation: a magnetic field- and current-basedsystem such as the CARTO™ 3 System (with current- andmagnetically-driven or receptive electrodes) available from BiosenseWebster, and as generally shown with reference to one or more of U.S.Pat. No. 6,498,944 entitled “Intrabody Measurement,” U.S. Pat. No.6,788,967 entitled “Medical Diagnosis, Treatment and Imaging Systems,”and U.S. Pat. No. 6,690,963 entitled “System and Method for Determiningthe Location and Orientation of an Invasive Medical Instrument,” theentire disclosures of which are incorporated herein by reference, or thegMPS™ system or MEDIGUIDE™ technology from St. Jude Medical, Inc., andas generally shown with reference to one or more of U.S. Pat. No.6,233,476 entitled “Medical Positioning System,” U.S. Pat. No. 7,197,354entitled “System for Determining the Position and Orientation of aCatheter,” and U.S. Pat. No. 7,386,339 entitled “Medical Imaging andNavigation System,” the entire disclosures of which are incorporatedherein by reference. In accordance with a magnetic field-based system,the catheter can be configured to include field sensors (e.g., coils)responsive to a magnetic field transmitted through the body of thepatient to sense the strength of the field at a particular location andtransmit a representative signal to an external computer or processor.Such field sensors can comprise one or more conductive coils (not shown)located on or within the catheter shaft 12 in a magnetic field-basedsystem. As noted above, a combination electric field-based and magneticfield-based system such as the CARTO™ 3 System (available from BiosenseWebster), and as generally shown with reference to U.S. Pat. No.7,536,218 entitled “Hybrid Magnetic-Based and Impedance-Based PositionSensing,” the entire disclosure of which is incorporated herein byreference, can be used. In accordance with a combination electricfield-based and magnetic field-based system, the catheter can includeboth electrodes 32, 34, 36 as one or more impedance-based electrodes andone or more magnetic field-sensing coils. For example and withoutlimitation, electrodes 32, 34, 36 can be used in accordance with thesystems and methods described in prior filed commonly owned U.S. patentapplication Ser. No. 13/087,203, entitled “System and Method forRegistration of Multiple Navigation Systems to a Common CoordinateFrame” and filed on Apr. 14, 2011, and U.S. patent application Ser. No.13/231,284, entitled “Catheter Navigation Using Impedance and MagneticField Measurements” and filed on Sep. 13, 2011, each of which is herebyincorporated by reference in its entirety as though fully set forthherein.

Referring now to FIG. 3, a cross-sectional view of a medical device 100in accordance with a second embodiment of the disclosure is generallyillustrated. The medical device 100 is substantially identical to themedical device 10 of FIGS. 1-2, except that the distal end 126 of thesecond segment 116 is formed in the shape of a curled pigtail instead ofa tip electrode having a substantially spherical or hemispherical end.The distal end 126 of the second segment 116 can comprise a highlyflexible plastic in accordance with an embodiment of the disclosure. Forexample and without limitation, the distal end 126 of the second segment116 can comprise a polymer. The polymer can comprise, for example andwithout limitation, polyether block amides such as those sold under thetrademark PEBAX® and generally available from Arkema France. Althoughpolyether block amides are mentioned in detail, the polymer can compriseany number of other polymers such as PTFE, FEP, polyurethane, PP, PVC,polyether-ester (for example a polyether-ester elastomer such asARNITEL® available from DSM Engineering Plastics), polyester (forexample a polyester elastomer such as HYTREL® available from DuPont),polyamide (for example, DURETHAN® available from Bayer or CRISTAMID®available from Elf Atochem), elastomeric polyamides, blockpolyamide/ethers, silicones, polyethylene, Marlex high-densitypolyethylene, linear low density polyethylene (for example REXELL®),PEEK, PI, PEI, or other suitable materials, or mixtures, combinations,or copolymers thereof. Additionally, in at least one embodiment, thedistal end 126 of the second segment 16, 116 may be an electrode, and,accordingly, may be made from a flexible, conductive material, such as aconductive polymer. Although these particular materials are mentioned indetail, the distal end 126 of the second segment 116 can comprise anynumber of other materials in accordance with various embodiments of thedisclosure. A second segment 116 formed in the shape of a pigtail can bea particularly atraumatic configuration for the distal end of the secondsegment 116 since it can distribute force over a larger region than adistal end, such as a distal end 26 described above, having asubstantially spherical or hemispherical end.

Referring now to FIGS. 2-4, medical device 10, 100 may also comprise acoil 38. The coil can be configured to prevent collapsing of anirrigation lumen disposed within the coil as described in more detailhereinbelow. The coil 38 comprises a means for maintaining the amount offorce transmitted by the second segment 16, 116 to the first segment 14and/or tissue contacting at least a portion of the second segment 16,116 after an application of the second critical force to the secondsegment 16, 116 that is sufficient to cause buckling of the secondsegment 16, 116. Without the means for maintaining the amount of forcetransmitted by the second segment 16, 116 after an application of thesecond critical force to the second segment 16, 116 that is sufficientto cause buckling of the second segment 16, 116, the medical device 10,100 would tend to collapse and provide a somewhat constant forceafterwards. The coil 38 provides a more uniform force after buckling ofthe medical device 10, 100 than without. The coil 38 does notsignificantly increase the second critical force required to cause thesecond, distal segment 16, 116 to buckle. However, coil 28 is configuredto allow second segment 16, 116 to transmit force in the range of atleast about 20 grams-force to about 50 grams-force even afterapplication of the second critical force to the second segment 16, 116sufficient to cause buckling of the second segment 16, 116. In this way,coil 38 is configured to allow medical device 10, 100 to buckle to avoidperforation of cardiac tissue by limiting the amount of force that canbe applied by the second segment 16, 116 to the cardiac tissue, whilestill ensuring that the medical device 10, 100 is able to transmit aminimum amount of force required to create transmural lesions in thetissue. Such an embodiment including coil 38 can result in thepredictable and/or recoverable buckling of the medical device 10, 100.The amount of force generated by bending and/or compressing the coil 38can be used to fine-tune the second critical force that is sufficient tocause buckling of the second segment 16. More significantly in someembodiments of the disclosure, coil 38 can be configured to preventcollapsing of an irrigation lumen within the coil 38 before, after,and/or during a buckling of the second segment 16, 116. Coil 38 may beseparate from both the proximal, first segment 14 and from the distal,second segment 16, 116 by use of a reflow procedure, for example. Coil38 may be disposed within the second segment 16, 116 of medical device10, 100. For example and without limitation, the coil 38 may be disposedradially inwardly of the inner surface 24, 124 of the second segment 16,116.

The coil 38 can comprise any number of suitable materials, including,for example and without limitation, metals, metal alloys, polymers,metal-polymer composites, and the like. Some examples of materialsinclude stainless steel, nickel-chromium alloy, nick-chromium-ironalloy, cobalt alloy, platinum, low durometer plastic, and the like.Additional examples of material include straightened super elastic orlinear elastic alloy (e.g., nickel-titanium or Nitinol) wire, oralternatively, a polymer material, such as a high performance polymer.The coil 38 can be formed of round wire or flat ribbon ranging indimensions to achieve the desired characteristics such as flexibility,and can be wound in a generally helical fashion by conventional windingtechniques. For example and without limitation, the thickness of thecoil 38 can be varied along the length of the coil 38. In someembodiments of the disclosure, the coil 38 can comprise a quad-filercoil which is comprised of multiple coils (e.g., about four coils) thatare interleaved together about a common radial axis. A quad-filer coilcan be more flexible, have a lower buckling force, and have the abilityto operate even in the case of failure (e.g., breakage) of a singlecoil. In some embodiments of the disclosure, the coil 38 can comprise atri-filer coil which is comprised of multiple coils (e.g., about threecoils) that are interleaved together about a common radial axis. Atri-filer coil can also be more flexible, have a lower buckling force,and have the ability to operate even in the case of failure (e.g.,breakage) of a single coil. Although quad-filer and tri-filer coils arementioned in detail, there may be any number of multiple coilsinterleaved together for the coil 38 in accordance with variousembodiments of the disclosure (e.g., N-filer coil, where N is the numberof coils interleaved together). Additionally, a support structureproviding similar functionality to that of coil 38 may include a braidedset of wires in place of, or in addition to, coil 38.

The coil 38 has a proximal end 40 and a distal end 42. The pitch ofadjacent turns of the coil 38 can be tightly wound so that each turntouches the succeeding turn, or the pitch can be set such that the coil38 is wound in an open fashion. The pitch of adjacent turns of the coil38 can be substantially constant along the length of the coil 38 fromthe proximal end 40 to the distal end 42 in accordance with anembodiment of the disclosure and as shown in FIG. 2. In accordance withother embodiments of the disclosure, the pitch between adjacent turns ofthe coil 38 can vary along the length of the coil 38 from the proximalend 40 to the distal end 42. A variable pitch of the coil 38 can bepreferable in some embodiments of the disclosure to help ensure that anybuckling of second segment 16, 116 occurs in a smooth and/or continuousfashion or radius, rather than a sharp 90 degree bend or kink that mightotherwise occur. A variable pitch of the coil 38 can also be preferablein some embodiments of the disclosure to help ensure that any bucklingof second segment 16, 116 occurs at a particular location along thelength of the second segment 16, 116. For example and withoutlimitation, the pitch or the spacing between adjacent turns of the coil38 can be greater near the distal end 42 of the coil 38 than theproximal end 40 of the coil 38, as generally illustrated in FIG. 3, tohelp ensure that the buckling of second segment 16, 116 occurs closer tothe distal end 42 of the coil 38 than to the proximal end 40 of the coil38 in a smooth, continuous fashion or radius. Accordingly, the coil 38can have a relatively tight pitch at the proximal end 40 of the coil 38and a relatively wide pitch at the distal end 42 of the coil 38.

In accordance with some embodiments of the disclosure, the coil 38 canbe wound so that the diameter of each turn is substantially constantalong the length of the coil 38 from the proximal end 40 to the distalend 42. In accordance with other embodiments of the disclosure, thediameter of each turn can vary along the length of the coil 38 from theproximal end 40 to the distal end 42. A variable diameter of the coil 38may be preferable in some embodiments to help ensure that any bucklingof second segment 16, 116 occurs in a smooth and/or continuous fashionor radius, rather than a sharp 90 degree bend or kink that mightotherwise occur. A variable diameter of the coil 38 can also bepreferable in some embodiments of the disclosure to help ensure that anybuckling of second segment 16, 116 occurs at a particularly locationalong the length of the second segment 16, 116. For example and withoutlimitation, a first diameter D₁ of the turns of the coil 38 at theproximal end 40 can be greater than a second diameter D₂ of the turns ofthe coil 38 at the distal end 42, as generally illustrated in FIG. 3, tohelp ensure that the buckling of second segment 16, 116 occurs closer tothe distal end 42 of the coil 38 than to the proximal end 40 of the coil38 in a smooth, continuous fashion or radius. Accordingly, the coil 38can have a relatively larger diameter D₁ at the proximal end 40 of thecoil 38 and a relatively smaller diameter D₂ at the distal end 42 of thecoil 38.

At least a portion of the proximal end 40 of the coil 38 can be attachedto the second segment 16, 116 in some embodiments of the disclosure. Atleast a portion of the distal end 42 of the coil 38 can be attached tothe second segment 16, 116 in some embodiments of the disclosure. Theproximal and distal ends 40, 42 of the coil 38 can be attached to thesecond segment 16, 116 using any suitable attachment mechanism, forexample, a solder joint, adhesive, thermal bonding, mechanical bonding,welding, and the like. For example and without limitation, approximatelytwo to three turns of the coil 38 at both the proximal end 40 and at thedistal end 42 can be attached to the second segment 16, 116. Inaccordance with an embodiment of the disclosure, two of electrodes 32,34, 36 can be swaged upon each portion of the coil 38 that is attachedto the second segment 16, 116 at proximal and distal ends 40, 42 of thecoil 38 in order to help maintain the position of coil 38. Although thecoil 38 is described as being attached to the second segment 16, 116 inaccordance with some embodiments of the disclosure, in other embodimentsof the disclosure, the coil 38 can be allowed to float more freely,lacking one or more fixed attachment points to the second segment 16,116. The use of a relatively free floating coil 38 in accordance withsome embodiments of the disclosure can be configured to allow the facesof the ends of the coil 38 to not necessarily remain perpendicular tothe longitudinal axis A of the medical device 10, which can potentiallyalleviate “bunching” of the coil 38 where the turns overlap each otherduring flexing of the coil 38.

The coil 38 is further configured to maintain the hoop strength of themedical device 10, 100. Hoop strength refers to the ability of a tubularcomponent to maintain its circumferential structural integrity. Invarious embodiments and still referring to FIGS. 2-4, the medical device10, 100 may further comprise a fluid lumen 44. The fluid lumen 44 may beconfigured for use with fluid (e.g., saline) irrigation to cool theelectrode 30 and target tissue interface during radiofrequency (RF)ablation. Irrigation fluid can be pumped through the second segment 16,116 of the medical device 10, 110 via the fluid lumen 44. The fluidlumen 44 is disposed radially inwardly of the coil 38 in the secondsegment 16, 116. However, the fluid lumen 44 generally extends along thelength of both the first segment 14 and the second segment 16 inaccordance with an embodiment of the disclosure. The fluid lumen 44 canbe located in the approximate center of the shaft 12. For example, thefluid lumen 44 can be defined by polyimide tubing in accordance with anembodiment of the disclosure. For example and without limitation, thepolyimide tubing may comprise braided polyimide tubing. Polyimide tubinghas a very high strength, but can easily kink and/or deform if it isbent beyond a critical angle or radius. The coil 38 is configured toavoid kinking or other deformation of the fluid lumen 44 that couldotherwise cut off the flow of fluid through the fluid lumen 44 duringuse of the medical device 10, 100, including during buckling of thesecond segment 16. The coil 38 is configured to support the hoopstrength of the fluid lumen 38 during buckling, which allows for an openpathway in which the fluid lumen 44 resides.

Referring now to FIG. 5, the medical device 10, 100 can further includea deflection preference element 46 configured to preferentially bucklethe second segment 16, 116 in a select manner during application of acritical force thereto in accordance with an embodiment of thedisclosure. In other words, the deflection preference element 46 cancomprise means for allowing the second segment 16, 116 to preferentiallybuckle in a select manner. For example and without limitation, thedeflection preference element 46 can comprise a curve at a selectlocation along the length of the medical device 10, 100. The curve canbe relatively shallow in accordance with an embodiment of thedisclosure. For example and without limitation, the curve can be in therange of up to about 15 degrees. For another example and withoutlimitation, the curve can be in the range of about 5 degrees to about 25degrees. Again, even though those specific exemplary curves arementioned in detail, the range of degrees for the curve can be greateror smaller in accordance with various embodiments of the disclosure. Forexample and without limitation, the curve can be defined by the angle αbetween the longitudinal axis A of the first segment 14 and alongitudinal axis A′ of the distal-most portion of the second segment16, 116 as generally illustrated in FIG. 5. The deflection preferenceelement 46 can be configured to pre-instruct the second segment 16, 116of the medical device 10, 100 the direction and/or orientation ofbuckling. It may be preferable in accordance with an embodiment of thedisclosure to include a deflection preference element 46 in order tocontrol the location and direction or orientation of the buckling of thesecond segment 16, 116 along the length of the medical device 10, 100.For example and without limitation, it may be preferable for thebuckling to occur away from the proximal end 28, 128 of the secondsegment 16, 116 and/or it may be preferable for the buckling to occur ina particular direction away from the longitudinal axis A of the medicaldevice 10, 100. Although these buckling configurations are mentioned indetail, the medical device 10, 100 is configured to buckle in anylocation along the length of the medical device 10, 100 and/or in anydirection and can accommodate on-axis forces.

The medical device 10, 100 can further comprise a force/contact sensorassembly 48 configured to detect an amount of force provided by themedical device 10, 100. Referring now to FIG. 6, for example and withoutlimitation, the force/contact sensor assembly 48 can include one or moresensors 50 disposed generally adjacent a base portion of the electrode30. The sensors 50 can be configured to measure pressure applied to thetip of the electrode 30 and provide a pressure signal indicative of themeasured pressure, with the sensors 50 including a predeterminedsensitivity. The electrode 30 and the remainder of medical device 10,100 can include a predetermined flexibility so that force applied to theelectrode 30 can be determinable as a function of the predeterminedsensitivity and the pressure signal. For example and without limitation,the force/contact sensor assembly 48 can be substantially similar to thesensor assembly described in U.S. Patent Application Publication No.2010/0168620 entitled “System And Method For Measuring Force And TorqueApplied To A Catheter Electrode Tip,” which is hereby incorporated byreference in its entirety as though fully set forth herein. Theforce/contact sensor assembly 48 can also be substantially similar toand/or incorporate features of the sensors described in U.S. PatentApplication Publication No. 2008/0249522 entitled “Irrigated CatheterWith Improved Fluid Flow,” U.S. Patent Application Publication No.2008/0275428 entitled “Optic-Based Contact Sensing Assembly and System,”and/or International (PCT) Published Patent Application No. WO2010/078453 entitled “Optic-Based Contact Sensing Assembly and System,”the entire disclosures of which are incorporated herein by reference.The force/contact sensor assembly 48 can also be substantially similarto and/or incorporate features of the sensors described in U.S. PatentApplication Publication No. 2011/0022045 entitled “Ablation ElectrodesWith Capacitive Sensors for Resolving Magnitude and Direction of ForcesImparted to a Distal Portion of a Cardiac Catheter,” U.S. PatentApplication Publication No. 2008/0161796 entitled “Design of AblationElectrode With Tactile Sensor,” U.S. Patent Application Publication No.2008/0015568 entitled “Dynamic Contact Assessment for ElectrodeCatheters,” U.S. Patent Application Publication No. 2007/0123764entitled “Systems and Methods for Assessing Tissue Contact,” and U.S.Patent Application Publication No. 2007/0100332 entitled “Systems andMethods for Electrode Contact Assessment,” the entire disclosures ofwhich are incorporated herein by reference.

In accordance with some embodiments of the disclosure, the sensorassembly 48 can be operatively connected to a signal converter (notshown) and/or an operator interface (not shown), which can furtherinclude a computer and a display, for processing the pressure signalsreceived in connection with positioning and contacting targeted tissue.This information can be processed to determine the contact force exertedon the electrode 30. A calibration system (not shown) can be furtherprovided to readily correlate the pressure measurements to the externalforce or torque on the electrode 30. A navigation, visualization, and/ormapping system, such as the ENSITE NAVX™ system mentioned above andgenerally available from St. Jude Medical, Inc., can be integratedand/or used with the sensor assembly 48.

Although one exemplary force/contact sensor assembly 48 is described indetail, other force/contact sensor assemblies can be used in accordancewith other embodiments of the disclosure. For example and withoutlimitation, another approach for sensing contact is to assess the degreeof electrical coupling, for example, in an electrical coupling index(ECI) between a sensing element and the surface, as seen by referenceto, for example, U.S. patent application Ser. No. 12/253,637, now U.S.Patent Application Publication No. 2009/0163904 entitled “System andMethod for Assessing Coupling Between an Electrode and Tissue,” which isincorporated herein by reference in its entirety as though fully setforth herein. The ENSITE NAVX™ system mentioned above and generallyavailable from St. Jude Medical, Inc. can estimate contact between anablation electrode and the targeted tissue based on local impedancemeasurements, and this calculation is termed the ECI. In other words,the ECI can be derived from the complex impedance measurement. Researchhas shown that there can be a correlation between the ECI and forcecontact, and a computer can be used to process the ECI information todetermine the contact force exerted on the electrode 30 in someembodiments of the disclosure. The ECI can be subject to variabilitybased on changes to properties associated with patient bodies (e.g.,differences in body temperature among patients) and components of thesystem (e.g., differences resulting from the use of different ablationcatheters).

In some embodiments of the disclosure, the medical device 10, 100 can beconfigured into an implicit contact force sensor. Under this approach,monitoring a bend angle between critical sections of the segments 14,16, 116 of the medical device 10, 100 can be used for sensing forceand/or contact. For example, in those embodiments of the disclosurehaving about four electrodes as generally illustrated in FIG. 4, theproximal two electrodes 34, 36 can be disposed on a first criticalsection 37, and the distal two electrodes 30, 32 can be disposed on asecond critical section 39. A bend angle β between the axial line L₁defined by electrodes 34, 36 and the axial line L₂ defined by electrodes30, 32 may be proportional to contact force. The bend angle β can becontinuously monitored using a visualization, navigation, and/or mappingsystem such as those systems available under the name ENSITE NAVX™ (akaENSITE™ ‘Classic’ as well as newer versions of the ENSITE™ system,denoted as ENSITE VELOCITY™) and available from St. Jude Medical, Inc.In other words, the electrode pairs 30, 32, and 34, 36 may serve asposition and/or orientation sensors configured to generate a signalindicative of the bend angle β. Alternatively, if magnetic field sensors(e.g., coils) are disposed in the medical device 10, 100 for use with amagnetic tracking system such as the system available under the nameMEDIGUIDE™ and available from St. Jude Medical, Inc., the bend angle βbetween the lines L₁, L₂ defined by electrodes 30, 32, 34, 36 can becontinuously monitored using the magnetic tracking system. A calibrationsystem (not shown) can be provided to readily correlate the measurementsfor the bend angle β to the external force or torque on the medicaldevice 10, 100, and/or a computer can be used to process the bend angleβ to determine the contact force exerted on the medical device 10, 100in some embodiments of the disclosure.

In accordance with an embodiment of the disclosure, the pressuremeasurements and/or force measurements can be used to modify and/orcontrol the advancement of the medical device 10, 100 to achieve adesired amount of contact/force between the medical device 10, 100 andtargeted tissue. Movements of the chest and heart, due to respiratoryand pumping function, can cause problems in ensuring optimal contactbetween the medical device 10, 100 and the targeted tissue. For exampleand without limitation, the targeted tissue may be moving as with, forexample, the beating of the heart. The use of the pressure measurementsand/or force measurements can help ensure constant contact and/ordesired amount of force between the medical device 10, 100 and targetedtissue by advancing and/or retracting the medical device 10, 100 aselect distance as needed to ensure contact and/or desired force withthe moving body structure. Such an embodiment of the disclosure may beespecially useful in connection with robotically controlled medicaldevices. In accordance with such an embodiment, an electronic controlunit (ECU) (not shown) can be used in connection with the sensorassembly 48 and the medical device 10, 100. A display device (not shown)can also be used in connection with the sensor assembly 48 and themedical device 10, 100 and the ECU.

The ECU comprises a programmable microprocessor or microcontroller, butcan alternatively comprise an application specific integrated circuit(ASIC). The ECU can include a central processing unit (CPU) and aninput/output (I/O) interface through which the ECU can receive inputdata (e.g., pressure measurements from sensor assembly 48) and cangenerate output data (e.g., force measurements and/or select distancesfor advancement and/or retraction of medical device 10, 100). The ECUcan also have a memory. The input data and output data acquired andgenerated by the ECU can be stored in the memory of the ECU. Asdescribed above, the input data can include the pressure measurementsobtained by the sensor assembly 48. The input data can further includeinformation regarding the sensitivity of the sensor assembly 48 and/orthe flexibility of the medical device 10, 100 or portions thereof. Asdescribed above, the output data can include select distances foradvancement and/or retraction of medical device 10, 100. The ECU anddisplay device can also be connected to a control system (not shown).The control system can be configured to adjust theadvancement/retraction of the medical device 10, 100 based at least inpart on the force/contact sensing in accordance with an embodiment ofthe disclosure. For example, if the sensor assembly 48 (or other systemdescribed herein) senses a decrease in contact/force, then the controlsystem may be configured to advance the medical device 10, 100 towardthe targeted tissue. However, if the sensor assembly 48 senses anincrease in contact/force, then the control system may be configured toretract the medical device 10, 100 away from the targeted tissue. Thesensor assembly 48 can thus provide feedback which can be implemented ina control algorithm executed by the ECU and/or control system toautomatically control the movement (e.g., advancement/retraction) of themedical device 10, 100. As a safety measure, when the pressure readingsfrom the sensor assembly 48 exceed a predetermined or select thresholdvalue, the control system can be configured to prevent further actuationand/or advancement of the medical device 10, 100. Alternatively oradditionally, the sensed pressure and/or force can be displayed to theuser with or without a warning (e.g., visual or audible). In someembodiments, a robotic or remote catheter guidance system, such as thatdescribed in one or more of the following, may be employed to performsome, or all, of the above stated functions: U.S. Patent ApplicationPublication No. 2009/0247942, published Oct. 1, 2009 and entitled“Robotic Catheter Manipulator Assembly”; U.S. Patent ApplicationPublication No. 2009/0247944, published Oct. 1, 2009 and entitled“Robotic Catheter Rotatable Device Cartridge”; U.S. Patent ApplicationPublication No. 2009/0247993, published Oct. 1, 2009 and entitled“Robotic Catheter System”; U.S. Patent Application Publication No.2009/0248042, published Oct. 1, 2009 and entitled “Model Catheter InputDevice”; International Published Patent Application No. WO 2009/120982,published Oct. 1, 2009 and entitled “Robotic Catheter System WithDynamic Response”; U.S. Patent Application Publication No. 2010/0256558,published Oct. 7, 2011 and entitled “Robotic Catheter System”; and U.S.patent application Ser. No. 12/933,063 filed Sep. 16, 2010 and entitled“Robotic Catheter System Input Device”, the entire disclosures of whichare incorporated herein by reference.

Although at least five embodiments of this disclosure have beendescribed above with a certain degree of particularity, those skilled inthe art could make numerous alterations to the disclosed embodimentswithout departing from the spirit or scope of this disclosure. Alldirectional references (e.g., upper, lower, upward, downward, left,right, leftward, rightward, top, bottom, above, below, vertical,horizontal, clockwise, and counterclockwise) are only used foridentification purposes to aid the reader's understanding of the presentdisclosure, and do not create limitations, particularly as to theposition, orientation, or use of the disclosure. Joinder references(e.g., attached, coupled, connected, and the like) are to be construedbroadly and can include intermediate members between a connection ofelements and relative movement between elements. As such, joinderreferences do not necessarily infer that two elements are directlyconnected and in fixed relation to each other. It is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative only and not limiting.Changes in detail or structure can be made without departing from thespirit of the disclosure as defined in the appended claims.

Any patent, publication, or other disclosure material, in whole or inpart, that is said to be incorporated by reference herein isincorporated herein only to the extent that the incorporated materialsdoes not conflict with existing definitions, statements, or otherdisclosure material set forth in this disclosure. As such, and to theextent necessary, the disclosure as explicitly set forth hereinsupersedes any conflicting material incorporated herein by reference.Any material, or portion thereof, that is said to be incorporated byreference herein, but which conflicts with existing definitions,statements, or other disclosure material set forth herein will only beincorporated to the extent that no conflict arises between thatincorporated material and the existing disclosure material.

What is claimed is:
 1. A medical device comprising: a shaft comprisingan axis and comprising a first, proximal segment and a second, distalsegment, wherein the second, distal segment includes a proximal end anda distal end, a first electrode disposed on the distal end of thesecond, distal segment; a second, ring electrode disposed on the second,distal segment, the second electrode being disposed proximally of thefirst electrode and disposed proximally of a portion of the shaft of thesecond, distal segment; a third, ring electrode disposed on the second,distal segment, the third electrode being disposed proximally of thesecond electrode, the first, second, and third electrodes comprisingelectrically conductive material; wherein the first segment isconfigured to buckle upon application of a first critical force thereto;and wherein the second segment includes an outer surface and an innersurface and the second segment is configured to buckle upon applicationof a second critical force thereto, wherein the second critical force islower than the first critical force; and a coil disposed radiallyinwardly of the inner surface of the second segment configured tomaintain an amount of force transmitted by the second segment to tissuecontacting the second segment after an application of the secondcritical force to the second segment, the coil being disposed betweenthe second, ring electrode and the third, ring electrode, wherein theamount of force transmitted by the second segment to the tissue afterbuckling is limited to the second critical force as the device isadvanced over a distance toward the tissue.
 2. The medical device ofclaim 1, wherein the second critical force is in the range of about 40grams-force to about 100 grams-force.
 3. The medical device of claim 1,wherein the second segment has a hardness between about 25 and about 35on a Shore D scale.
 4. The medical device of claim 1, wherein the secondsegment has a distal end and a proximal end, and wherein the distal endof the second segment is formed in the shape of a pigtail.
 5. Themedical device of claim 1, further comprising at least one electrodedisposed on the second segment.
 6. The medical device of claim 1,wherein the second segment is configured to transmit force in the rangeof at least about 20 grams-force to about 50 grams-force to tissuecontacting the second segment after application of the second criticalforce to the second segment.
 7. The medical device of claim 1, whereinthe coil has a proximal end and a distal end and wherein spacing betweenadjacent turns of the coil is greater at the distal end of the coil thanthe proximal end of the coil.
 8. The medical device of claim 1, whereinthe coil has a proximal end and a distal end and wherein a firstdiameter of the coil at the proximal end is greater than a seconddiameter of the coil at the distal end.
 9. The medical device of claim8, wherein at least a portion of the proximal end of the coil is weldedto the second segment and wherein at least a portion of the distal endof the coil is welded to the second segment.
 10. The medical device ofclaim 1, wherein the second segment includes a curve at a selectlocation along a length of the medical device.
 11. The medical device ofclaim 10, wherein the curve is in the range from about 5 degrees toabout 25 degrees.
 12. The medical device of claim 1, further comprisinga fluid lumen disposed radially inwardly of the coil.
 13. The medicaldevice of claim 1, further comprising a force/contact sensor configuredto detect an amount of force provided by the medical device.
 14. Themedical device of claim 1, wherein the second segment comprises a firstcritical section on which a first plurality of electrodes are disposedand a second critical section on which a second plurality of electrodesare disposed, and wherein the medical device further comprises a sensorconfigured to generate a signal indicative of a bend angle between thefirst critical section and the second critical section of the secondsegment.
 15. The medical device of claim 1, wherein the shaft furthercomprises a third segment, wherein the third segment is configured tobuckle upon application of a third critical force thereto, wherein thethird critical force is different than the first critical force andwherein the third critical force is different than the second criticalforce.
 16. The medical device of claim 1, wherein the coil is free andunattached relative to the second segment.
 17. A medical devicecomprising: a shaft comprising an axis and comprising a first, proximalsegment and a second, distal segment, a first ablation electrodedisposed on a distal end of the second segment of the shaft; a second,ring electrode disposed on the second, distal segment, the secondelectrode being disposed proximally of the first, ablation electrode anddisposed proximally of a portion of the shaft of the second, distalsegment; a third, ring electrode disposed on the second, distal segment,the third electrode being disposed proximally of the second electrode; afourth, ring electrode disposed on the second, distal segment, thefourth electrode being disposed proximally of the third electrode, thefirst, second, third, and fourth electrodes comprising electricallyconductive material; a coil disposed radially inwardly of an innersurface of the second segment, the coil being disposed between thesecond, ring electrode and the third, ring electrode; wherein the firstsegment is configured to buckle upon application of a first criticalforce thereto; wherein the second segment is configured to buckle uponapplication of a second critical force thereto, wherein the secondcritical force is lower than the first critical force; and wherein thecoil is configured to maintain an amount of force transmitted by thesecond segment to tissue contacting the second segment after applicationof the second critical force to the second segment so as to provide atransmitted amount of force between (i) a first amount in a range of atleast about 20 grams-force to about 50 grams-force required to create atransmural lesion during ablation therapy using the ablation electrodeand (ii) a second, minimum amount in the range of about 40 grams-forceto about 100 grams-force that can cause perforation of the tissue,wherein the first amount is less than the second, minimum amount, andwherein the amount of force transmitted by the second segment to thetissue after buckling is limited to the second critical force as thedevice is advanced over a distance toward the tissue.
 18. The medicaldevice of claim 17 wherein the coil is separate from both the firstsegment and the second segment; said device further comprising a fluidlumen disposed radially inwardly of the coil, said coil being configuredto prevent collapse of the fluid lumen within the coil due to bucklingof the second segment.
 19. A medical device comprising: a shaftcomprising an axis and comprising a first, proximal segment and asecond, distal segment, wherein the second, distal segment includes aproximal end and a distal end, a first electrode disposed on the distalend of the second, distal segment; a second, ring electrode disposed onthe second, distal segment, the second electrode being disposedproximally of the first electrode and disposed proximally of a portionof the shaft of the second, distal segment; a third, ring electrodedisposed on the second, distal segment, the third electrode beingdisposed proximally of the second electrode, the first, second, andthird electrodes comprising electrically conductive material, whereinthe first segment is configured to buckle upon application of a firstcritical force thereto; and wherein the second segment is configured tobuckle upon application of a second critical force thereto, wherein thesecond critical force is lower than the first critical force; and meansin said second segment between the second, ring electrode and the third,ring electrode for maintaining an amount of force transmitted by thesecond segment to tissue contacting the second segment after anapplication of the second critical force to the second segment, whereinthe amount of force transmitted by the second segment to the tissueafter buckling is limited to the second critical force as the device isadvanced over a distance toward the tissue.
 20. The medical device ofclaim 19, further comprising means for preferentially buckling thesecond segment in a select manner.